The present invention relates to an electrical connector. More specifically, the present invention relates to high input/output density connectors, such as surface mount connectors using ball grid array (BGA) technology.
The recent drive for smaller, more functional electronic equipment, particularly personal portable devices, has created an ongoing need for miniaturization of all components, especially electrical connectors. Efforts to miniaturize connectors have included reducing the pitch between terminals in single or double row linear connectors. This permits a relatively larger number of connections in the ever decreasing space allotted for connectors on circuit substrates. The drive for smaller electronic equipment has also been accompanied by a recent preference for surface mount techniques (SMT) for mounting components on circuit boards. However, because reducing the pitch between terminals increases the risk of bridging adjacent solder pads during the reflow of solder paste, SMT has been pushed to its limits for high volume, low cost operations.
To satisfy the need for increased terminal density in SMT, array connectors have been proposed. In particular, as described in PCT Application No. PCT/US97/18066, filed Oct. 7, 1997, entitled High Density Connector and Method of Manufacture, incorporated herein by reference, ball grid array (BGA) connectors have become a reliable and efficient technique for mounting high density electrical connectors on substrates using SMT. BGA connectors have an insulative connector housing. One side of the connector housing has a matrix of spherical solder balls, positioned to engage the conductive paths of a circuit substrate. The opposite side of the connector housing has a corresponding matrix of contact terminals, which extend through the connector housing and connect electrically to the solder balls. These contact terminals are designed to engage another BGA connector, similarly connected to another substrate, thus permitting board-to-board interconnection.
Because of their low profile, BGA connectors may be used to interconnect a number of various types of circuit substrates, including flexible circuits. A flexible circuit is a pliable electrical conductor device in which conductive tracings are photolithographed on a base sheet of polyimide or polyester film, such as manufactured and sold by E.I. du Pont de Nemours and Co. under the trademarks xe2x80x9cKaptonxe2x80x9d (U.S. Pat. No. 3,781,596) or xe2x80x9cMylar.xe2x80x9d Because of their lightweight and ability to bend, flexible circuits are often used in confined locations, including portable computers and portable communication devices. The flexibility of the circuit substrate may introduce strain to the solder joint during handling. In addition, these confined locations make it difficult to dissipate heat generated by thermal cycling.
Thermal cycling can occur, for example, as the semiconductor device on the circuit substrate switches on and off. The electrical power dissipated within a semiconductor device heats the various components of the system, such as the substrate, the solder balls, the contacts, and the BGA connector housing. Due to differences in the coefficients of thermal expansion (CTE), temperature changes cause the various components to expand and to contract differently. This CTE differential may introduce mechanical stress in the solder joint between the connector and the substrate. Repeated thermal cycling can reduce the life of the solder joint. Although heat generated by thermal cycling is always a concern with substrate interconnections, it is especially important with BGA connectors because of their frequent use in confined locations. In addition, CTE differential effects become more pronounced as the size of the connector increases.
Therefore, a need exists to provide a BGA connector system with mechanical relief for absorbing strain created during thermal cycling.
The disadvantages of prior connector systems are overcome and significant advantages achieved in an electrical connector having a housing, and a first plurality of contacts in the housing that are adapted to be in electrical communication with a first substrate. The electrical connector further includes a second plurality of contacts in the housing that are adapted to be coupled to the first substrate. A first body of reflowable, electrically conductive material disposed on at least one of the first contacts, and a second body of material disposed on at least one of the second contacts. The first body is adapted to provide an electrical path between the connector and the first substrate, and the second body is adapted to provide relief for mechanical strain between the connector and the first substrate. The first and second bodies may be spherical. The second body may also be peripheral to the first body, and/or positioned along a series of contacts adjacent to an edge of the connector. The contacts of the electrical connector may form a matrix array. In this instance, the second body may be disposed on one or more of the contacts of the matrix array, and/or on one or more rows of contacts of the matrix array. The second body also may be disposed on one or more columns of contacts of the matrix array, and/or one or more corners of the matrix array. The second plurality of contacts may remain within the housing and not engage contacts of a mating connector. The electrical connector further may include a third plurality of contacts adapted to be in electrical communication with a second substrate, and a fourth plurality of contacts adapted to be coupled to the second substrate. The third and fourth contacts may be adapted to be removably connected to the first and second contacts. The electrical connector also may include a third body of reflowable, electrically conductive material disposed on at least one of the third contacts. The third body may be adapted to provide an electrical path between the connector and the second substrate. The electrical connector also may include a fourth body of reflowable, electrically conductive material disposed on at least one of the fourth contacts. The fourth body may be adapted to provide relief for mechanical strain between the connector and the second substrate caused by a temperature change.
The invention also includes a device for coupling and absorbing strain between a first and second substrate. The device includes a first electrical connector, and a second electrical connector mateable with the first connector. The first electrical connector has a first housing having a first side and a second side, a first plurality of contacts extending from the first side of the first housing, and a first body of material disposed on at least one of the first contacts. The material is adapted to be connected to the first substrate. The second electrical connector has a second housing having a first side and a second side, a second plurality of contacts extending from the first side of the second housing, and a second body of material disposed on at least one of the first contacts. The material is adapted to be connected to the second substrate. Also, the second side of the second housing is adapted to be removably connected to the second side of the first housing, and a portion of the first and second plurality of contacts do not mate. The first and second body of material may be spherical, and may be composed of conductive material. Also, the portion of the first and second plurality of contacts may be embedded within the housings.
The invention further includes a method for providing mechanical strain relief to a connector system. The method includes providing an electrical connector having a first and second plurality of contacts, disposing a first body of reflowable, electrically conductive material on at least one of the first contacts, and disposing a second body of reflowable, electrically conductive material on at least one of the second contacts. The first body is adapted to provide an electrical path between the connector and a first substrate, and the second body is adapted to provide relief for mechanical strain between the connector and the first substrate. The second body may be peripheral the first body, and may be positioned along a series of contacts adjacent to an edge of the connector. The inventive method may include mounting the electrical connector on the substrate. Also, the contacts may form a matrix array. The inventive method may include disposing the second body on one or more of the contacts of the matrix array, and disposing the second body on one or more rows of contacts of the matrix array. The inventive method may further include disposing the second body on one or more columns of contacts of the matrix array, and/or disposing the second body in one or more corners of the matrix array.
The invention includes an improved ball grid array connector having a plurality of contacts in a housing. The improved connector is engeagable with a mating connector and the improvement includes a portion of the plurality of contacts that remain within the housing so as not to engage the mating connector.